What's the name of this component in AppKit?

Question

I want to know the name of sidebar-like component below. Screenshot of AirMail
Screenshot of Tweetbot

Both of them have same width and similar appearance, so I thought that the component is available in AppKit but I couldn't find it in documentation by myself.

I've googled about NSTabViewController and NSSplitViewController, but I don't think they are the answer I want.

If you have any idea, please tell me!

Answer 1

Airmail is using a subclass of NSTableView as you can see in the following screenshot showing Airmail and F-Script Anywhere side-by-side:

F-Script Anywhere is generally very useful for finding out which UI components an app is using. Another good alternative is the new Debug View Hierachy feature in Xcode. To use this, open any macOS project in Xcode, then attach the debugger to the app you would like to inspect (Debug - Attach to Process) and click the Debug View Hierarchy button.